Laboratory evaluation of heat-and-moisture exchangers

Abstract

We conducted a laboratory study on six commercially available heat and moisture exchangers in order to determine and compare their water retaining efficiency and their contribution to airway resistance. The Gambro-Engström Edith Flex device was the most desirable of the six devices we evaluated in terms of its water retaining efficiency. The NMI Pneumoist 1 and the Siemens Servo Humidifier 153 units had good water retaining capacity but their higher airflow resistance need close monitoring, especially after prolonged clinical use. The Pall HME 15-22 and the Portex Humid-Vent 1 devices were also efficient in water retaining capacity. The Pall also demonstrated low airflow resistance and the minimum increase in airflow resistance after water immersion. The pathogen filtering capacity of the Pall should also be considered an additional advantage, especially in infected patients. The Terumo Breathaid device performed worst of all six devices, but it was still better than no HME at all.

A novel method of evaluation of three heat-moisture exchangers in six different ventilator settings

“…Most of the efficiency formulas are based on gravimetric humidity measurements and involve the unfavorable aspects of the gravimetric method [16,21,22,27,28]. The formulas calculating the efficiency of humidification during on-line measurements are relatively uncommon and inadequate.…”

“…Several studies have been done to test resistances of HMEs; however, there are some shortcomings in their methodology, such as separation of HMEs from the actual breathing system, a maximum of four resistance measurements in a 24-h measurement period using dry air flow, and the use of constant air flow in the measurement of expiratory resistance [16,[18][19][20][21][22][23][24][25][26][27][28]40]. In this study, the shortcomings of these studies have been eliminated; the resistance measurements were done continuously in conditions closely resembling clinical conditions.…”

“…Several experimental studies have been done to test these properties of HMEs, where gravimetric humidity measurements and resistance measurements have been made outside the ventilation system by using a constant dry air flow [11,16,18,[20][21][22][23][24][25][26][27][28]. Gravimetric humidity measurements are only reliable during long-term studies and give only an average value.…”

“…The temperature level should be between approximately 29 and 35°C [1,2,[30][31][32][33][34][35]. The humidity output of HMEs in occlusion has been reported to occur between 10 and 28 mg/1 [11,20,22,27,28,37,38]. The humidity output of HMEs in occlusion has been reported to occur between 10 and 28 mg/1 [11,20,22,27,28,37,38].…”